Urbanization effects on temporal variations of avian haemosporidian infections

Urbanization is an important human-driven process that leads to biodiversity loss and alters the interactions between organisms, including disease transmission. Although urbanization affects both host and vector communities, the effects on vector-borne pathogens are still poorly understood. Here, we monitored variation in prevalence and richness of three common blood parasites in birds (Plasmodium, Haemoproteus and Leucocytozoon) from localities with different land uses (urban, rural and natural) during two consecutive years (2013 and 2014). Overall, 1400 juvenile house sparrows (Passer domesticus) from 15 localities in southern Spain were included in this study. Haemoproteus and Leucocytozoon prevalence was higher in 2013 than in 2014, particularly in urban and natural habitats for the case of Leucocytozoon. Prevalence was correlated between years for Haemoproteus and Leucocytozoon, independently of the habitat. Additionally, rural habitats harboured significantly higher Haemoproteus lineage richness compared to urban and natural habitats during 2014. Leucocytozoon lineage richness was negatively correlated between years in rural habitats but positively correlated in urban and natural habitats in comparison. Parasite lineages found in birds were homogeneously distributed along habitats and years and the common lineages prevalence were not influenced by them. Our results highlight different patterns of infection depending on the parasite genera probably related to the composition and density of vector communities. The specific reproductive environmental requirements of the different groups of vectors involved in the transmission may be affected by climatic conditions and landscape features.

Fuel loads of Neotropical migrant songbirds on autumn passage through the Darién region of Colombia: Influence of migratory distance, route, ENSO, age and body size

Available energy stores determine stopover length, migration speed and likely survival in migrating birds. We measured energy stores by estimating fuel load in 11 species of Neotropical migrant songbirds in the Darién of Colombia over five years. We evaluated 1) whether individuals flying further from breeding origin arrived with smaller fuel loads, 2) if the ENSO (El Niño-Southern Oscillation) cycle affected fuel load and 3) if species known to migrate mostly overwater arrived with less fuel relative to those migrating overland. Breeding origin, inferred from feather δ2H values, only had a significant positive effect on fuel load in Swainson’s Thrush (Catharus ustulatus). Veery (Catharus fuscescens) and Swainson’s thrush had higher and lower fuel loads, respectively, in El Niño years. Multi-species mixed-effects models revealed support for larger fuel loads in larger-bodied species and in species taking overwater routes, contrary to our prediction. Across species, we found no support for common effects of breeding origin or ENSO on fuel loads, in contrast to community-wide effects of migration route and body-size. In general, the variables considered here explained little of the variance in fuel loads, suggesting that inter-individual differences likely have a greater impact than broad-scale factors in our study system.

Do wild-caught urban house sparrows show desensitized stress responses to a novel stressor?

While urbanization exposes individuals to novel challenges, urban areas may also constitute stable environments in which seasonal fluctuations are buffered. Baseline and stress-induced plasma corticosterone (cort) levels are often found to be similar in urban and rural populations. Here we aimed to disentangle two possible mechanisms underlying such pattern: (i) urban environments are no more stressful or urban birds have a better ability to habituate to stressors; or (ii) urban birds developed desensitized stress responses. We exposed wild-caught urban and rural house sparrows (Passer domesticus) to combined captivity and diet treatments (urban versus rural diet) and measured corticosterone levels both in natural tail feathers and in regrown homologous ones (cort_f). Urban and rural house sparrows showed similar cort_f levels in the wild and in response to novel stressors caused by the experiment, supporting the growing notion that urban environments are no more stressful during the non-breeding season than are rural ones. Still, juveniles and males originating from urban populations showed the highest cort_f levels in regrown feathers. We did not find evidence that cort_f was consistent within individuals across moults. Our study stresses the need for incorporating both intrinsic and environmental factors for the interpretation of variation in cort_f between populations.

Summary: Corticosterone in natural and regrown feathers was similar between urban and rural birds. Sex and age related to corticosterone in regrown feathers. Feather corticosterone was not consistent across different moults.